1. Field of the Invention
This invention relates to the field of transportation. More particularly, this invention relates to highway motor freight vehicles; it reduces the air drag on these vehicles, thus improving their efficiency. When attached to existing truck or truck tractor cabs, this invention changes air flow patterns around both the cab and the body behind the cab in such a fashion as to reduce turbulent air flow. The energy required to generate and sustain turbulence is thus reduced. Since turbulent air flow patterns serve no useful purpose, and since the energy to generate and sustain them is provided by the vehicles engines, their reduction improves the efficiency of these vehicles. Thus, vehicles using the present invention can either go faster with the same power or travel at the same speed with reduced power, or be operated using a combination of increased speed and reduced power.
2. Description of the Prior Art
Sp far as is known, the improved air drag reducer described and claimed herein has not been known before. The existence of air drag itself on highway vehicles, and particularly on truck tractor-semitrailer combinations, where the semitrailer is a closed van type, has been known nearly as long as the vehicles have been in use. A comprehensive study of air drag on truck tractor-semitrailer combinations and how to reduce it was performed in 1953 at the University of Maryland. That study, and others, showed that rounded corners, smooth surfaces, closing of the gap between the truck tractor and the semitrailer and similar design features would substantially reduce air drag on these vehicles. Rather than following these design principles, however, motor freight vehicles have subsequently been mostly designed to be more rather than less bluff; this has principally been the result of legal length limits. Concurrently, the Interstate highway system plus improved high horsepower engines have enabled these vehicles to be operated for long periods at sustained high speeds. The greater bluffness and higher speeds combine to increase air drag.
Several devices have been introduced to reduce this air drag. These include the device of U.S. Pat. No. 2,863,695 by Alexander F. Stamm, those of U.S. Pat. Nos. 3,241,876, 3,309,131, and 3,348,873 all by Walter Seldon Saunders, and that of U.S. Pat. No. 3,695,673 by James H. Meadows.
The apparatus of U.S. Pat. No. 2,863,695 employs air flow through conduits and thus differs markedly from the present invention, which employs air flow over exterior surfaces to achieve a reduction in air drag.
The devices and apparatus of the other Patents by Messrs. Saunders and Allen also differ from the present invention in several ways. The present invention is readily adjustable to provide a maximum of air drag reduction for a truck tractor when used with semitrailers of differing heights. The other inventions are only efficient for one increment of height difference between cab roof and semitrailer roof. Also, when a truck tractor with one of these other inventions installed is used in combination with a flat bed semitrailer or is driven with no semitrailer at all, drag is increased rather than decreased. The present invention is readily adjustable so that it does not increase air drag when it is mounted on a truck tractor which is either driven with no semitrailer or is used in combination with a flat bed or low bed semitrailer.
The present invention redirects air flow patterns in such a way as to produce substantially less force on the cab of the using vehicle at the attach points than certain of the devices described in Mr. Saunders Patents. Thus, the present invention does not require that the cab roof be reinforced as part of the installation procedure, as is necessary for these other devices.
The present invention differs from those of Messrs. Saunders and Allen in that their inventions utilize the front faces of airfoils to redirect air flow patterns, tolerating or even enhancing turbulence behind their devices. The present invention uses both upper front and lower rear faces of an airfoil to redirect air flow patterns and reduce turbulence in the region behind the airfoil.
The present invention attaches an airfoil above the vehicles cab roof such that a gap is maintained between the airfoil and the cab roof. This invention is configured so that air flows through this gap and is redirected with a reduction in turbulence over the following parts of the vehicle. This gap and the concommitant utilization of the lower rear surface of the airfoil to redirect air flow are of special importance in cross winds. Wind tunnel tests have shown that other cab top configurations and other devices mounted on cab roofs reduce air drag when there is a direct head wind but that they increase air drag when driving in a cross wind is simulated. The present invention does not increase air drag in a cross wind.